The first step in all of my paintings, whether it is a character or an environment, is to lay down the basic shapes. These shapes become the building blocks of the illustration, and without them it is easier for your illustration to fail (image 1).
After I have the basic shapes down I go ahead and start adding in some of the details, since most of this illustration is detail oriented and there are not many large shapes (image 2).

I usually try and put down windows a row at a time, that way it is easier to get them to line up (image 3 & 4).